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What value resistor to cure earth noise?

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Re: What value resistor to cure earth noise?

Postby garrettendi » Fri Jun 08, 2018 10:56 am

Do you think something might be wrong with my amp then?
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Re: What value resistor to cure earth noise?

Postby Hugh Robjohns » Fri Jun 08, 2018 11:16 am

Oh no! I've kick-started your paranoia again! :lol:

Without knowing all the details about the kind of interference you experienced I can't possibly say... and in any case, you've solved the problem.

Clearly, commercially manufactured products shouldn't interfere with each other and the EMC legislation is intended to ensure that's the case... but you have to be realistic and practical about these things.

There was a time when CD-players often caused interference to a radio tuner sat on top in a hi-fi rack... and that was understandable given the very high frequencies flying around inside a CD player, but the designers soon learned how to prevent that from happening.

A traditional guitar amp shouldn't have anything rattling around at RF frequencies, but can do so under certain fault conditions. However, a modelling guitar amp or one with built-in digital effects will have a lot of high-frequency stuff inside, and if the construction is not done right it's quite possible that some of that might leak out to interfere with sensitive gear nearby.

But if everything works properly when separated by a foot or two I really wouldn't worry about it too much.

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Re: What value resistor to cure earth noise?

Postby garrettendi » Fri Jun 08, 2018 11:17 am

Thanks Hugh! Panic over!

It works absolutely fine in every other regard, so I won't rush out to the amp repairman just yet!
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Re: What value resistor to cure earth noise?

Postby The Elf » Fri Jun 08, 2018 12:31 pm

I'd forgotten that Orchid did that neat little transformer. I'll grab one of those anyway.

Thanks all of you guys.
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Re: What value resistor to cure earth noise?

Postby garrettendi » Fri Jun 08, 2018 12:32 pm

Do Orchid pay for all this advertising? :lol:

I've said it before and I'll say it again... Orchid saves the day once more!
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Re: What value resistor to cure earth noise?

Postby ef37a » Fri Jun 08, 2018 12:48 pm

Further to the hum pickup issue with the "Velcro'ed" transformer?

People have done this with wall rats and line lumps back of racks. Now I do not have the rabid dislike of these things that many on the SoS strength display but they DO radiate a pretty strong hum field. The older, 50Hz jobs are now rarely sold* but there must still be many thousands still about. SMPSUs should be screened to stop this but it would still be wise to keep them a good foot or more from mic circuits!

*Illegal to be sold now in EU but will we become a dumping ground in 3-4 years time?!

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Re: What value resistor to cure earth noise?

Postby Davelet » Fri Jun 08, 2018 9:10 pm

ef37a wrote:Further to the hum pickup issue with the "Velcro'ed" transformer?

People have done this with wall rats and line lumps back of racks. Now I do not have the rabid dislike of these things that many on the SoS strength display but they DO radiate a pretty strong hum field. The older, 50Hz jobs are now rarely sold* but there must still be many thousands still about. SMPSUs should be screened to stop this but it would still be wise to keep them a good foot or more from mic circuits!

*Illegal to be sold now in EU but will we become a dumping ground in 3-4 years time?!

Dave.

The trouble with EMC legislation IMO is that it's all self-certification by the manufacturer, with many test conditions determined by them, e.g., when testing for emissions, the angles of the device with respect to the receiver which leads me onto a true story ...

Years ago I was working on a company I worked for had developed a USB-connected and powered device and we just couldn't get the thing to pass radiated emissions. It had to be plugged into a laptop to test it and we assumed that the laptop was OK and couldn't possibly be emitting as it was made by a respected manufacturer who I won't name (but it might rhyme with "hell"). Well, after lots of head scratching it *did* turn out that it was the laptop that was emitting like hell outside the limits but only within a certain narrow angle.


Going back to in-line power supplies (aka "wall warts"). In my experience, SMPS based ones are far worse for audio interference than traditional 50 Hz transformers. Don't think manufacturers will screen SMPS in-line PSUs adequately - they will do the bare minimum that allows them to pass the legislative thresholds in tests that they have designed and conducted. Those tests are unlikely to include all a wide range of angles from the PSU - it could be only 2 or 3, and certainly unlikely to include all power loads on the PSU (which is important, as SMPS switching frequency varies with load). And they will definitely not include start-up tests which is when they are at their noisiest. I had one a few years back that would take out DAB reception within a 5 metre radius when it was first plugged in.
The reason that the bare minimum is done is to avoid finding problems, as if found they then have to be fixed, and the fixes are expensive (margins are tiny).

I would assume that you can still legally sell 50 Hz transformers where the product *requires* it for noise reasons? E.g., at one extreme I'm sure medical equipment would have an exemption. But what about AM radio receivers? They just can't receive anything in the presence of an SMPS.
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Re: What value resistor to cure earth noise?

Postby The Elf » Tue Jun 12, 2018 7:57 pm

Yup, the Orchid isolator has fixed the noise and the mains earth is now reconnected! Phew!!! :beamup:
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Re: What value resistor to cure earth noise?

Postby Hugh Robjohns » Tue Jun 12, 2018 8:27 pm

Yay! Glad it's sorted and the synth made safe again. :clap: :thumbup: The solution is nearly always that simple and straightforward, and yet it remains the biggest mystery to the greatest number of people. Between the forum and direct emails I must answer at least half a dozen different ground-loop query posts every month...

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Re: What value resistor to cure earth noise?

Postby garrettendi » Tue Jun 12, 2018 8:36 pm

Woohoo for Orchid!
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Re: What value resistor to cure earth noise?

Postby Jumpeyspyder » Tue Jun 12, 2018 9:41 pm

Glad its all safe & quiet :)
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Re: What value resistor to cure earth noise?

Postby The Elf » Tue Jun 12, 2018 9:46 pm

Well I've got to admit that I have no idea what is going on in terms of why the noise is there, but all I wanted was it fixed and made safe. Job done.

Thanks to all! :clap: :thumbup:
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Re: What value resistor to cure earth noise?

Postby Martin Walker » Wed Jun 13, 2018 3:37 pm

Hugh Robjohns wrote:Yay! Glad it's sorted and the synth made safe again. :clap: :thumbup: The solution is nearly always that simple and straightforward, and yet it remains the biggest mystery to the greatest number of people. Between the forum and direct emails I must answer at least half a dozen different ground-loop query posts every month...

I used to reply to so many at one point that my SOS byline was 'You hum it, I'll trace the ground loop' ;)


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